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A new process to restore the condition of spent cathodes could make recycling of lithium-ion batteries cheaper. The process, developed by nanoengineers from the University of California at San Diego, is more environmentally friendly than today’s methods; uses greener ingredients, consumes 80 to 90% less energy and emits about 75% less greenhouse gases.
The researchers detail their work in a paper published on 12 November a Joule.
The process works particularly well on lithium iron phosphate cathodes, or LFPs. Batteries made with LFP cathodes are less expensive than other lithium-ion batteries because they don’t use expensive metals like cobalt or nickel. LFP batteries also have a longer life and are safer. They are widely used in power tools, electric buses, and energy networks. They are also the preferred battery for Tesla’s Model 3.
“Given these advantages, LFP batteries will have a competitive advantage over other lithium-ion batteries on the market,” said Zheng Chen, professor of nanoengineering at UC San Diego.
The problem? “It’s not convenient to recycle them,” Chen said. “It’s the same dilemma with plastics: the materials are cheap, but the methods of recovering them aren’t.”
The new recycling process developed by Chen and his team could reduce these costs. It works at low temperatures (60 to 80 C) and ambient pressure, making it less energy hungry than other methods. Additionally, the chemicals it uses – lithium salt, nitrogen, water, and citric acid – are inexpensive and benign.
“The whole remanufacturing process works under very safe conditions, so we don’t need special safety precautions or special equipment. That’s why we can make this cost so low for battery recycling,” said first author Panpan Xu, a postdoctoral researcher at Chen’s laboratory.
The researchers first recycled the commercial LFP cells until they lost half of their energy storage capacity. They took apart the cells, collected the cathode powders and soaked in a solution containing lithium salt and citric acid. Then they washed the solution with water, dried the powders and heated.
Researchers created new cathodes from the powders and tested them in both button cells and bag cells. Their electrochemical performance, chemical composition and structure have all been completely restored to their original state.
During the battery cycle, the cathode undergoes two major structural changes that are responsible for its decline in performance. The first is the loss of lithium ions, which creates empty sites called vacancies in the cathode structure. The other occurs when the iron and lithium ions change points in the crystal structure. When this happens, they can’t go back easily, so the lithium ions get trapped and can no longer flow through the battery.
The process restores the cathode structure by replenishing the lithium ions and facilitating the return of the iron and lithium ions to their original stains. The latter is achieved by using citric acid, which acts as a reducing agent, a substance that donates an electron to another substance. Citric acid transfers electrons to iron ions, making them less positively charged. This minimizes the electronic repulsion forces that prevent the iron ions from returning to their original points in the crystal structure and also releases the lithium ions into circulation.
Although the overall energy costs of this recycling process are lower, the researchers say more studies are needed on the logistics of collecting, transporting and handling large quantities of batteries.
“Figuring out how to optimize this logistics is the next challenge,” Chen said. “And that will bring this recycling process closer to industry adoption.”
Source of the story:
Materials provided by University of California – San Diego. Original written by Liezel Labios. Note: The content can be changed by style and length.
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